linux-kernel - Re: [PATCH 0/4] riscv: uaccess: optimizations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240705112502.GC9231@willie-the-truck>
Date: Fri, 5 Jul 2024 12:25:03 +0100
From: Will Deacon <will@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Jisheng Zhang <jszhang@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mark.rutland@....com
Subject: Re: [PATCH 0/4] riscv: uaccess: optimizations

On Sun, Jun 30, 2024 at 09:59:36AM -0700, Linus Torvalds wrote:
> On Tue, 25 Jun 2024 at 11:12, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > But yes, it would be lovely if we did things as "implement the
> > low-level accessor functions and we'll wrap them for the generic case"
> > rather than have every architecture have to do the wrapping..
> 
> Btw, to do that _well_, we need to expand on the user access functions
> a bit more.

[...]

> Will/Catalin - would that
> 
>         src = masked_user_access_begin(src);
> 
> work on arm64? The code does do something like that with
> __uaccess_mask_ptr() already, but at least currently it doesn't do the
> "avoid conditional entirely", the masking is just in _addition_ to the
> access_ok().

I think we'd need to go back to our old __uaccess_mask_ptr()
implementation, where kernel addresses end up being forced to NULL. In
other words, revert 2305b809be93 ("arm64: uaccess: simplify
uaccess_mask_ptr()"). If we then want to drop the access_ok() entirely,
we'd probably want to use an address that lives between the two TTBRs
(i.e. in the "guard region" you mentioned above), just in case somebody
has fscked around with /proc/sys/vm/mmap_min_addr.

Will